1. Field of the Invention
The present invention relates to a method of operating a hydrogen and power generation system comprising at least a reforming device and a combination fuel cell and ion pump, wherein the system is selectively operable in a hydrogen generation mode and an electricity generation mode when an anode thereof is supplied with a reformed gas from the reforming device.
2. Description of the Related Art
Fuel cells are a system for generating DC electric energy from an electrochemical reaction caused when anode and cathode are supplied with a fuel gas, i.e., a gas mainly containing hydrogen, and an oxygen-containing gas, i.e., a gas mainly containing oxygen.
For example, a solid polymer electrolyte fuel cell includes a power generation cell having a membrane electrode assembly (MEA), which is sandwiched between separators. The electrolyte electrode assembly comprises an electrolytic membrane in the form of a polymer ion exchange membrane, and anode and cathode that are disposed on respective opposite sides of the electrolytic membrane. Usually, a predetermined number of membrane electrode assemblies and a predetermined number of separators are stacked together in a fuel cell stack, for use in vehicles such as automobiles.
The fuel gas that is supplied to the fuel cells normally comprises hydrogen gas, which is generated from a raw material such as a hydrocarbon material by a reforming device. Generally, the reforming device operates to produce a reform raw gas from a raw hydrocarbon material, such as methane, LNG, or the like, and then to reform the reform raw gas according to a water vapor reforming process, a partial oxidation reforming process, or an automatic thermal reforming process, for thereby generating the reformed gas (fuel gas).
The fuel gas generated by the reforming device needs to be converted into highly pure hydrogen gas (refined hydrogen gas), and may be compressed for storage. To this end, a combination fuel cell and ion pump, as disclosed in Japanese Laid-Open Patent Publication No. 2007-505472 (PCT), is employed.
The combination fuel cell and ion pump comprises an electrochemical cell having an anode inlet for receiving a fuel, an anode outlet for discharging the fuel, a cathode inlet for receiving an oxidizer, a cathode outlet for discharging at least one of the oxidizer, refined oxygen, and refined hydrogen, a first connector, and a second connector, and a controller for supplying electric charges to the first and second connectors in order to cause the electrochemical cell to act as a fuel cell for generating electricity, and for supplying potentials to the first and second connectors to cause the electrochemical cell to act as at least one of a hydrogen pump for refining hydrogen and an oxygen pump for refining oxygen.
The combination fuel cell and ion pump is selectively operable in a hydrogen producing (hydrogen pump) mode and an electricity generating (fuel cell) mode. In either of these modes, the anode outlet discharges an anode off-gas containing unburned hydrogen gas. In order to effectively utilize the unburned hydrogen gas contained in the anode off-gas, the anode off-gas must be supplied to a combustor of the reforming device for evaporating reforming pure water, or be used as a heat source for increasing the temperature of the reform raw fuel.
Temperature variations of the combustor are likely to affect the reaction temperatures of a reforming reaction and a CO shift reaction, thereby tending to increase the CO concentration within the reformed gas, for example. For performing a stable gas reforming reaction, therefore, it is necessary to minimize temperature changes in the combustor insofar as possible.